leandrof/linux
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

x86/bugs, kvm: Introduce boot-time control of L1TF mitigations

Browse Source 
Introduce the 'l1tf=' kernel command line option to allow for boot-time
switching of mitigation that is used on processors affected by L1TF.

The possible values are:

  full
	Provides all available mitigations for the L1TF vulnerability. Disables
	SMT and enables all mitigations in the hypervisors. SMT control via
	/sys/devices/system/cpu/smt/control is still possible after boot.
	Hypervisors will issue a warning when the first VM is started in
	a potentially insecure configuration, i.e. SMT enabled or L1D flush
	disabled.

  full,force
	Same as 'full', but disables SMT control. Implies the 'nosmt=force'
	command line option. sysfs control of SMT and the hypervisor flush
	control is disabled.

  flush
	Leaves SMT enabled and enables the conditional hypervisor mitigation.
	Hypervisors will issue a warning when the first VM is started in a
	potentially insecure configuration, i.e. SMT enabled or L1D flush
	disabled.

  flush,nosmt
	Disables SMT and enables the conditional hypervisor mitigation. SMT
	control via /sys/devices/system/cpu/smt/control is still possible
	after boot. If SMT is reenabled or flushing disabled at runtime
	hypervisors will issue a warning.

  flush,nowarn
	Same as 'flush', but hypervisors will not warn when
	a VM is started in a potentially insecure configuration.

  off
	Disables hypervisor mitigations and doesn't emit any warnings.

Default is 'flush'.

Let KVM adhere to these semantics, which means:

  - 'lt1f=full,force'	: Performe L1D flushes. No runtime control
    			  possible.

  - 'l1tf=full'
  - 'l1tf-flush'
  - 'l1tf=flush,nosmt'	: Perform L1D flushes and warn on VM start if
			  SMT has been runtime enabled or L1D flushing
			  has been run-time enabled
			  
  - 'l1tf=flush,nowarn'	: Perform L1D flushes and no warnings are emitted.
  
  - 'l1tf=off'		: L1D flushes are not performed and no warnings
			  are emitted.

KVM can always override the L1D flushing behavior using its 'vmentry_l1d_flush'
module parameter except when lt1f=full,force is set.

This makes KVM's private 'nosmt' option redundant, and as it is a bit
non-systematic anyway (this is something to control globally, not on
hypervisor level), remove that option.

Add the missing Documentation entry for the l1tf vulnerability sysfs file
while at it.

Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Jiri Kosina <jkosina@suse.cz>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lkml.kernel.org/r/20180713142323.202758176@linutronix.de
This commit is contained in:
Jiri Kosina
2018-07-13 16:23:25 +02:00
committed by Thomas Gleixner
parent fee0aede6f
commit d90a7a0ec8
5 changed files with 165 additions and 19 deletions
Download Patch File Download Diff File Expand all files Collapse all files

44
arch/x86/kernel/cpu/bugs.c
View File

@@ -665,7 +665,11 @@ void x86_spec_ctrl_setup_ap(void)
#undef pr_fmt
#define pr_fmt(fmt) "L1TF: " fmt
/* Default mitigation for L1TF-affected CPUs */
enum l1tf_mitigations l1tf_mitigation __ro_after_init = L1TF_MITIGATION_FLUSH;
#if IS_ENABLED(CONFIG_KVM_INTEL)
EXPORT_SYMBOL_GPL(l1tf_mitigation);
enum vmx_l1d_flush_state l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_AUTO;
EXPORT_SYMBOL_GPL(l1tf_vmx_mitigation);
#endif
@@ -677,6 +681,20 @@ static void __init l1tf_select_mitigation(void)
if (!boot_cpu_has_bug(X86_BUG_L1TF))
return;
switch (l1tf_mitigation) {
case L1TF_MITIGATION_OFF:
case L1TF_MITIGATION_FLUSH_NOWARN:
case L1TF_MITIGATION_FLUSH:
break;
case L1TF_MITIGATION_FLUSH_NOSMT:
case L1TF_MITIGATION_FULL:
cpu_smt_disable(false);
break;
case L1TF_MITIGATION_FULL_FORCE:
cpu_smt_disable(true);
break;
}
#if CONFIG_PGTABLE_LEVELS == 2
pr_warn("Kernel not compiled for PAE. No mitigation for L1TF\n");
return;
@@ -695,6 +713,32 @@ static void __init l1tf_select_mitigation(void)
setup_force_cpu_cap(X86_FEATURE_L1TF_PTEINV);
}
static int __init l1tf_cmdline(char *str)
{
if (!boot_cpu_has_bug(X86_BUG_L1TF))
return 0;
if (!str)
return -EINVAL;
if (!strcmp(str, "off"))
l1tf_mitigation = L1TF_MITIGATION_OFF;
else if (!strcmp(str, "flush,nowarn"))
l1tf_mitigation = L1TF_MITIGATION_FLUSH_NOWARN;
else if (!strcmp(str, "flush"))
l1tf_mitigation = L1TF_MITIGATION_FLUSH;
else if (!strcmp(str, "flush,nosmt"))
l1tf_mitigation = L1TF_MITIGATION_FLUSH_NOSMT;
else if (!strcmp(str, "full"))
l1tf_mitigation = L1TF_MITIGATION_FULL;
else if (!strcmp(str, "full,force"))
l1tf_mitigation = L1TF_MITIGATION_FULL_FORCE;
return 0;
}
early_param("l1tf", l1tf_cmdline);
#undef pr_fmt
#ifdef CONFIG_SYSFS